1. Field of the Invention
The present invention generally relates to an optical system for a laser riflescope, and particularly relates to an optical system for a laser riflescope with a reduced number of optical elements while improving optical performance.
2. Description of Prior Art
As shown in FIG. 1, the optical system for a conventional riflescope generally includes an objective lens group 4, an erector lens group 5, an eyepiece lens (ocular lens) group 6 and a reticle 7 for facilitating aiming at the object. The optical system generally includes 9–12 spherical lenses in three groups. However, it is well known that, the spherical surfaces of the lenses are optically accurate only proximate to the optical axis while showing increasing refraction errors proportionally to the distance from the optical axis toward the periphery of the lens system, increasing with the distance from the optical axis. Such errors are both errors in deflection of the light beam as well as, more importantly yet, reflection errors. This phenomenon is known as spherical aberration. To eliminate the spherical aberration, additional correcting lenses are generally employed. However, this increases the potential for distortion, ghosting and flare. Further, the weight, bulk and complexity of the optical system are increased, since only glass lenses are generally used to assure compliance with the harsh environment reliability needs of the riflescope. This is particularly true for a laser riflescope that includes in its optical system, in addition to the objective lens group, the erector lens group and the eyepiece lens group, an LD (Laser Diode), an APD (Avalanche Photoelectric Diode), an LED (Light Emitting Diode) lens element and a plurality of prisms. Further, data processing and calculation programs are also provided in the laser riflescope for object distance calculation. All these components make the laser riflescope much heavier and bulkier than a common riflescope. Therefore, the rifle with the laser riflescope mounted thereon must be hold up by a supporter for facilitating stable aiming and shooting. This is rather inconvenient for the carry and usage of the rifle.
In addition, it is known that light rays of different colors do not focus at the same location after passing through a glass lens system. This phenomenon is known as chromatic aberration, which is present when images formed by different colors of light, which make up “white” light, are at different distances from the lens or are of unequal size. Chromatic aberration of a lens is seen as fringes of color around the image. This kind of aberration is eliminated by the optical design, conventionally combining different types of glass that will form several colors at the same point. However, this method further increases the weight and bulk of the riflescope.
Accordingly, a light weight and low bulk laser riflescope capable of eliminating both spherical aberration and chromatic aberration is desired to overcome the above disadvantages present in the prior art.